This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The long-term goal of our laboratory is to understand the mechanisms by which information is encoded within second messenger signals, including Ca2+ and cAMP. These signaling pathways are known to regulate diverse processes including cellular excitability, proliferation, and gene expression. Our understanding of Ca2+ signals has increased dramatically over the last 30 years, primarily due to the development of single-cell methods for measuring intracellular Ca2+. Our understanding of cAMP signals, however, has lagged behind, largely due to the lack of high-resolution, single-cell measurement techniques. Only recently have reliable approaches for measuring cAMP signals in single cells been developed. These approaches have provided an unprecedented view of cyclic nucleotide signals near the plasma membranes of several cell types. We have used these approaches to provide evidence suggesting that the effective diffusion coefficient of cAMP is considerably slower than had been previously thought (~10,000-fold slower movement than by free diffusion alone). In addition, elegant studies demonstrated that compartmentalized cAMP signals are critical for barrier function in pulmonary microvascular endothelial cells (PMVECs). Based upon these studies, we propose testing the following working hypothesis: phosphodiesterase activity, buffering, and anomalously slow cAMP diffusion localize cAMP signals in pulmonary microvascular endothelial cells.